The present invention relates to the field of aircraft landing gear including a raisable leg.
More particularly, the invention relates to landing gear in which the leg comprises a strut having a telescopic rod, the strut being hinged to the structure of an aircraft so as to pivot between high and low positions under drive from an associated actuator, said strut also being connected to the structure of the aircraft by hinged brace elements.
During the approach procedure of an aircraft, the extended landing gear generates wind resistance which increases as the landing gear legs move downwards, until they reach their locked gear-down position. These elements projecting from the bottom portion of the fuselage inevitably generate aerodynamic noise which is louder or quieter depending on the areas of the surfaces concerned.
Environmental constraints are leading aircraft builders to conduct increasing amounts of research in minimizing nuisance during approach procedures, and in particular aerodynamic noise. Very roughly, it is found nowadays that during an approach about 50% of aircraft noise comes from its engines, 25% from its structure (wings, flaps, tail), and 25% from the landing gear. These figures are the result of the considerable progress that has been achieved by engine manufacturers in reducing the noise made by jets, where jets used to be much noisier in the past. As a result, aerodynamic noise from the structure and the landing gear is contributing more to total noise than used to be the case.
The present invention seeks to design landing gear of the above-mentioned type that is of a shape that makes it possible to achieve a significant reduction in the aerodynamic noise generated while the landing gear is being extended, and in particular once the landing gear legs are in the down position.
Solving this problem is made complicated by the presence of portions of the landing gear which generally generate large amounts of turbulence, which turbulence constitutes a source of undesirable aerodynamic noise such as more or less strident whistling noises.
Clearly anti-turbulence deflector covers could be fixed on various parts that project, but that approach would not give full satisfaction insofar as the hinged zones would have to be left uncovered since otherwise the covers would interfere with the raising and lowering movements of the landing gear. This is particularly true of the main hinge between the arms of the brace that conventionally connects the landing gear leg to the structure of the aircraft, since firstly this hinged zone is of non-negligible dimensions, and therefore generates a great deal of turbulence, and secondly this hinged zone must also remain accessible when the landing gear is in its raised position insofar as it needs to be accessible for locking the landing gear in the raised position by means of a catch box fixed in the associated bay.
The state of the art is illustrated by document U.S. Pat. No. 2,180,462 A. That document describes main wing-mounted landing gear that is raised rearwards. Fairings forming part of an aerodynamic pod for surrounding the landing gear in the raised position are secured to the landing gear and cover it in part when the landing gear is in its lowered position. In an embodiment shown in FIGS. 8, 9, and 10, two fairing portions are installed on the branches of the scissors link, each of said portions being secured to a respective branch of the scissors link and serving to cover it.
Nevertheless, the fairing portions of the prior art system do not form an independent assembly. In addition, it should be observed that those portions are not hinged to each other, and that said portions do not serve to cover the hinge in the brace which, in that case, lies aft of the landing gear.
Reference can also be made to document EP-1 067 045 A which shows an arrangement of noise-reducing means in the form of fairings for deflecting air away from noise-generating portions.
The invention seeks to design landing gear that provides better performance, the shape of the landing gear enabling the aerodynamic noise generated during aircraft approach to be reduced to a great extent.
According to the invention, the problem is solved by an aircraft landing gear having a retractable leg, in which the leg comprises a strut with a telescopic rod, the strut being hinged to a structure of the aircraft in order to pivot between a gear-up position and a gear-down position under drive from an associated actuator, said strut also being connected to the structure of the aircraft via hinged brace elements, the landing gear including an independent low-noise fairing system that serves, when the leg is in the gear-down position, to cover the front of at least a portion of the hinge between the brace elements, said low-noise fairing system comprising a hinged fairing of two complementary portions connected to each other via a hinge whose axis is parallel to the axis of the corresponding hinge portion of said brace elements.
In this field, the term xe2x80x9clow noisexe2x80x9d is used to cover any acoustic treatment seeking to reduce noise.
In particular, for landing gear in which the brace elements comprise a main brace having a top arm hinged to the structure of the aircraft and a bottom arm hinged to an appendix associated with the strut of the landing gear leg, it is particularly advantageous to provide for the hinged fairing of the independent low-noise fairing system to act in the gear-down position to cover the front of the hinged zone between the top and bottom arms of the main brace.
In a preferred embodiment in this particular case, the hinged fairing comprises two complementary portions, in which a first portion is rigidly secured to the bottom arm of the main brace, and a second portion is connected via a connecting rod to the top arm of said brace, the four hinges concerned being arranged to form a hinged parallelogram.
It is then advantageous in the gear-down position, for the first portion of the hinged fairing to cover the bottom portion of the bottom arm of the main brace, the top portion of said bottom arm and the bottom portion of the top arm of said brace being covered by the second portion of said hinged fairing. In particular, the first portion of the hinged fairing terminates in a raised edge covering part of the hinged zone of the bottom arm of the main brace, the other part of said hinged zone being covered by a rigid fairing associated with the strut of the landing gear leg and also forming part of the independent low-noise fairing system.
Also advantageously, the second portion of the hinged fairing has a central bulge which, in the gear-down position, covers the hinge between the two arms of the main brace. In particular, said second portion of the hinged fairing presents longitudinal stiffeners on its inside for stiffening at least the central bulge zone.
Also preferably, the connecting rod is hinged between an end point of the second portion of the hinged fairing, and an associated fitting fixed to the top arm of the main brace at a point that completes the hinged parallelogram. In particular, the connecting rod pivots about its hinge on the fitting connecting it to the top arm, and about its point connected to the second portion of the hinged fairing through a range of about 150xc2x0 between the two positions of said connecting rod corresponding to the up and down positions of the landing gear leg.
The connecting rod may be a rigid rod, or in a variant it may be a rod that is adjustable in length or a resilient rod including a spring.
Lastly, it is advantageous in the gear-down position for the two complementary portions of the hinged fairing to be substantially in line one with the other.